cannot access hiddenfield value in masterpage on page_load event from child page

I'm trying to access a hiddenfield value from my masterpage that is set in my child aspx page, but cannot access it the masterpage codebehind page_load event.
Child aspx page:
    <asp:HiddenField runat="server" ID="hdnRptTitle" Value="Satellite Availability % Report" />
Master page:
    <asp:Label runat="server" ID="Label1" Style="text-align: right; font-size: xx-large; color: #808080"></asp:Label>
Master page code behind: This is where I want to set the text value of the report from the child page.
    protected void Page_Load(object sender, EventArgs e)         {             Label1.Text = hdnRptTitle.         }
There is no intellisense for the hdnRptTitle variable.
How ca ...